Finally, Autothrottles for the PT6

Innovative Solutions & Support is debuting its Pilatus PC-12 cockpit retrofit at NBAA 2015, including a clutchless autothrottle system for the airplane's PT6 engine.

Innovative Solutions & Support (IS&S) brought a highly modified Pilatus PC-12 to the NBAA 2015 indoor static display, although the changes are all in the cockpit and can’t be seen from the outside, which might mean waiting in line to get a peek inside. The big change will be somewhat subtle, until visiting pilots put their hand on the PC-12’s power lever, which is attached to an electronic and completely clutch-less autothrottle system. Also new in this PC-12 is something more obvious, the IS&S Future Flightdeck. While both can be seen in the PC-12 here, IS&S has also hooked the power lever up to a simulator, so visitors can see and feel it working.

If the PC-12’s upgraded avionics make the cockpit look a lot like the flight deck of a newer Eclipse 500/550, that is no coincidence, as IS&S is the avionics supplier for the Eclipse IFMS (integrated flight management system) cockpit. One Aviation’s new Eclipse 550s come with autothrottles, and this modification is also available as a retrofit for IFMS-equipped Eclipse 500s.

Autothrottles on a Pratt & Whitney Canada PT6-powered single-engine turboprop are somewhat unusual, because typically these devices require clutches and motors, and these take up a lot of space in a throttle quadrant, space that isn’t available on the PC-12. While not required for autothrottles, it’s also a lot easier to make them work with an engine with full-authority digital electronic control (Fadec); the PT6 uses traditional hydro-mechanical engine controls, and yet its IS&S autothrottle still manages to protect the engine from overtorquing and overtemping.

What makes IS&S’s autothrottle even more interesting is that it can be adapted to any PT6-powered airplane, although it will also require installation of IS&S’s Integrated Standby Unit (ISU) standby display, which runs the thrust computer software to make the autothrottle work. Thus the autothrottle system will be installable in almost any PC-12, from very early serial numbers to the latest PC-12 NG. IS&S is also looking at other popular PT6-powered airplanes for autothrottle upgrades, such as the King Air and TBM series. Adding the ISU also brings highly accurate RNP as well as WAAS LPV approach capability to aircraft with avionics that don’t permit these type of modern operations. The ISU includes a Beta 3 GPS receiver, and IS&S also offers a WAAS LPV upgrade for Bombardier’s CRJ series, using the ISU.

Autothrottle Details

While IS&S is reluctant to share in-depth technical details about its autothrottle system, company chairman Geoffrey Hedrick did provide some information. “We’ve come up with a very novel actuator,” he said. “We’ve developed one with no gears and no clutches, which is really revolutionary. On a PC-12, which never had enough room to put in a clutch pack for an autothrottle, this fits in there so easily.” He added, “It’s a direct-actuating actuator.” Pilots can easily override the autothrottle, something that is important for any such system, he said, “without any traditional slip clutches.”

With the ISU thrust computer, the PC-12 autothrottle will be able to control torque automatically in a climb, so the pilot will not have to continually move the power lever forward as torque drops. When the pilot moves the power lever manually and nears torque or temperature limits, the autothrottle has a built-in shaker system that vibrates to warn the pilot about reaching one of those limits, all part of the “iGuard” active engine protection system. The ISU also is programmed with windshear protection, which enables certification for use of autopilot to the middle marker or decision height, according to Hedrick. In the PC-12, the autothrottle offers other envelope protection features, for example, adding thrust in a low-airspeed condition. In a twin-engine installation, the autothrottles could offer other benefits, such as controlling thrust in an emergency. “How about adjusting the thrust so you always have Vmc [minimum control speed]?” Hedrick asked. “Before it gets into a Vmc situation, the throttles come back.”

IS&S hasn’t released pricing for the PC-12 autothrottle system yet, but Hedrick said it should be “quite a bit under $100,000,” which will include the ISU and its WAAS LPV benefits. Installation is fairly simple and involves adding an “end effector” to the power lever and a new fuel cam on the engine, something that takes about 10 minutes, according to Hedrick. “The connection between the throttle and the engine does not change,” he explained. “We don’t touch the connection between the throttle lever and the engine, and that makes certification [simple]. We just have to prove to the FAA that under no conditions will it prevent control of the engine.” IS&S expects certification of the PC-12 autothrottle in a few months, but this is being done in concert with certification of the new Future Flightdeck for the PC-12. Both new products should be available for installation starting in March.

The Future Flightdeck for the PC-12 will also include a unique oil-quantity gauge. IS&S engineers have figured out how to measure the difference between oil and oil foam, which occurs when the engine warms up. “We’re able to significantly mitigate the errors associated with foam,” Hedrick said.

The Future Flightdeck instrument panel includes two 10-inch primary flight displays in portrait format and a single 15-inch center multifunction display in landscape orientation. Each PFD contains its own independent FMS and GPS receiver. Also included are dual ADAHARS and air data computers.

The ISU in the PC-12 not only acts as a standby instrument but also is large enough to display an attitude indicator and HSI at the same time, plus other information such as glideslope and localizer. “It’s like a mini 10-inch PFD,” said Hedrick. A data concentrator is also part of the package, and this can send engine operating and trend information to the ground via datalink. The upgrade also replaces the engine gauge cluster in early PC-12s, with gauges displayed on the MFD. New remote-mount radios are included, as is ADS-B out and synthetic vision. The flight deck upgrade should shave 70 to 100 pounds from the PC-12’s empty weight. IS&S expects the PC-12 flight deck upgrade to cost less than $300,000.